Dharwar craton

The Dharwar craton in South India presents a natural cross-section of late-Archaean continental crust. There are three main structural zones: a root zone of highly heterogeneous petrology (from monzonite to granite) and texture (phenocryst accumulation), a "channel zone" where evidences of large scale magma ascent can be observed, and a zone of superficial intrusions, consisting in independent homogeneous intrusive bodies. In the root zone, mantle-derived magma underwent fractional crystallisation which was followed by mingling between the residual liquids and melts generated by anatexis of the surrounding gneissic basement.

The term Dharwaar supergroup is now used as synonymous with metamorphosed Archaean sediments and including all the schistose series below the eparchaean unconformity. The Dharwarian rocks are mostly unfossiliferous.

Lithology of the Dharwars

The rocks of this age show extremely complex nature with clastic and chemically precipitated sediments, volcanic and plutonic rocks - all of which show varying degrees of metamorphism. The majority of the rocks are often phyllites, schists and slates. There are hornblende-, chlorite-, haematite-, and magnetite- schists, felspathic schists: quartzites and highly altered volcanic rocks, like rhyolites and andesites turned into hornblende-schists; abundant and widespread granitic intrusions; crystalline limestones and marbles; serpentinous marbles; steatite masses; beds of jaspers and massive beds of iron and manganese oxides.

References

• Auvrey, Bernard, Mudlappa Jayananda, B Mahabaleswar, Hervé Martin and Jean-François Moyen. (1999) "From the Roots to the Top of a Granitic Body: The Closepet Granite of South India." Journal of Conference Abstracts, Vol. 4, No. 1, Symposium A08, Early Evolution of the Continental Crust. [1]

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